1. Field of the Invention
This invention relates to a vehicle assembly line, and more particularly to a vehicle assembly line including both automated assembly steps using robots and manual assembly steps.
2. Description of the Prior Art
In the vehicle manufacturing factory, automation has been promoted using robots, for instance. However, presently, automation has been realized mainly on the welding line and the coating line and, due to the complicated operations involved, there has been little automation on the assembly line which accounts for a major part of the manufacture of vehicles. However, progress in automation techniques, such as improvement in the performance of robots, has recently enabled automation of particular the assembly line steps and will gradually make it possible to increase the number of automated steps in the assembly line.
However, in automating one or more steps in an assembly line originally designed for manual operations, there arise difficulties due to, for instance, differences in ability and intrinsic nature between robots and human beings. For example, in an assembly line depending on manual labor, the line is generally formed of continuous feed conveyors which continuously feed works at a constant speed in order to avoid the danger which arises when a work is suddenly moved during the time it is being worked on by a worker. On the other hand, in the case of an assembly line depending on machines such as robots, the relative position between the work and the machine is important and therefore continuous feed is not suitable. Further, in the case of human workers, even if the positions of the components previously incorporated into the vehicle body are somewhat displaced from the predetermined positions, this does not substantially disrupt the following steps. However, in the case of automated operation, even slight displacement of previously incorporated components can disturb the following steps. Thus, it is difficult to change steps which have been manually performed to automated steps in a point-to-point fashion. This difficulty can be avoided by changing the line arrangement when the number of steps which can be automated reaches a certain number. However, this approach is not desirable from the viewpoint of cost.